1. Field of Invention
The embodiments of the present invention relate to a writing instrument that incorporates a granular material in its ink reservoir.
2. Description of the Related Art
An ink reservoir design of this type is known from U.S. Pat. No. 2,528,408. Specifically, this document discloses a nib pen whose ink reservoir is provided with a granular material. The structure of this material gives it a capillarity versus the ink that is suitable for obtaining a steady supply of ink to the nib. However, to obtain this capillarity, the granular material is sintered or has a distribution of grains inside the reservoir that is controlled. A sintered material that has a determined open porosity is difficult to produce in large runs in a reproducible manner. The sintering step then generates a considerable additional cost for the pen. In addition, filling the reservoir with the ink is made difficult, because the ink is slow to penetrate the interstices of the sintered granular material. Furthermore, when the granular material has to be distributed in a controlled manner in the form of separate grains in the reservoir, the grains must be placed in the reservoir in several steps, which represents an awkward and lengthy step in the manufacture of the pen. These disadvantages explain why no solution of this type is applied industrially in the present day. Specifically, the solutions chosen, particularly for porous writing tips, consist in placing a filler of synthetic fibrous material in the ink reservoir, or more recently, in storing the ink freely in the reservoir, that is to say with no filler material, and in fluidly connecting this reservoir to the tip by means of a controlled capillarity connector.
Furthermore, European patent application EP 1 510 560 discloses an ink composition that includes solid particles, particularly silica particles having a dimension less than 200 μm (microns). In this case, the silica particles form an integral part of the ink, that is to say that they are designed to be deposited with the colorants and the solvent of the ink on a writing medium such as paper. To prevent a writing instrument from being obstructed by the silica particles, the latter must represent less than 5% in weight of the ink. In these conditions, the capillarity of the reservoir of the writing instrument relative to the ink is not significantly improved.